The mechanism of action of the cytolytic toxin, streptolysin O (SLO), on mammalian erythrocytes will be investigated. The possibility that erythrocyte lipids are affected as a result of toxin action will be studied by comparing lipid extracts of SLO-treated and control cell membranes by thin layer chromatography. Neutral lipids, phospholipids, and glycolipids will be analyzed. In addition liposomes composed of combinations of membrane lipids will be examined to see whether SLO affects these artificial membrane vesicles. The adsorption of SLO to cell membranes will be studied using purified I-125 labelled toxin.